Refactor directed test infrastructue.

- Add hierarchy.  Tests now live in directories, each with its own
  CMakeFiles.txt.  Reduces merge conflicts.
- Change make_hip_executable -> build_hip_executable.
- Refresh docs.
- Enable some tests that were previously built but not run.

Change-Id: I8c5de3c954400bf233904282b8b42861a2b7c536

tests/src/runtimeApi/memory/hipMemcpyAsync2.cpp

@@ -0,0 +1,15 @@
+#include"test_common.h"
+
+#define SIZE 1024*1024
+
+int main(){
+    float *A, *Ad;
+    HIPCHECK(hipHostMalloc((void**)&A,SIZE, hipHostMallocDefault));
+    HIPCHECK(hipMalloc((void**)&Ad, SIZE));
+    hipStream_t stream;
+    HIPCHECK(hipStreamCreate(&stream));
+    for(int i=0;i<SIZE;i++){
+    HIPCHECK(hipMemcpyAsync(Ad, A, SIZE, hipMemcpyHostToDevice, stream));
+    HIPCHECK(hipDeviceSynchronize());
+    }
+}